Method and apparatus for print control

ABSTRACT

Embodiments of the present invention provide a method for use in a printing device, comprising outputting a test chart comprising a plurality of printed regions at respective ink densities, receiving an indication of a selected ink density, and determining one or more resources of the printing device according to the selected ink density to control one or more ink limits and a color separation of the printing device.

BACKGROUND

When printing onto a print media, particularly with liquid ink,controlling properties of the ink applied to the media are important toensure a quality of the printing. In particular, it is important tocontrol an amount of ink applied to the media. If too much ink isapplied to the media during printing then proper drying of the ink maynot occur.

In particular, it is important to control the amount of ink applied tomedia of different types to ensure that the amount of ink applied iswithin a drying capability of the printer for particular printingconditions. Furthermore it is important to control the amount of inkapplied to the media without degrading a quality of the print, such asloosing gamut.

It is an object of embodiments of the invention to at least mitigate oneor more of the problems of the prior art.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described by way of exampleonly, with reference to the accompanying figures, in which:

FIG. 1 shows a method according to an embodiment of the presentinvention;

FIG. 2 shows a test chart according to an embodiment of the invention;

FIG. 3 shows an apparatus according to an embodiment of the invention;

FIG. 4 is an illustration of linearization data according to anembodiment of the invention; and

FIG. 5 shows an apparatus according to a further embodiment of theinvention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Embodiments of the invention control a limit of ink applied to a printmedia during printing by a printing device. For print devices whichapply a liquid ink to the print media during printing such as, althoughnot limited to, inks containing a polymer dispersed in an aqueousliquid, it is important to ensure proper drying of the ink during theprinting process. In the case of inks containing the polymer, polymerlayer formation can only occur if substantially all water and solventshave been removed from the print media before reaching a curingtemperature. Therefore it is important to ensure the amount of inkapplied to the media during printing does not exceed a drying capabilityof the printing device.

Embodiments of the invention control one or more ink limits and a colourseparation of the printing device to ensure drying of the ink withoutaffecting other aspects of the print quality. Some embodiments of theinvention further control an amount of a pre-treatment substance appliedto the print media prior to application of the ink. The pre-treatmentsubstance may be used to control a dot gain of the ink applied to themedia. The amount of pre-treatment can cause print defects such as amixing of adjacent colours or desaturated areas at a border of a colourarea.

FIG. 1 illustrates a method 100 according to an embodiment of theinvention.

In step 110 a test chart is output by a printing device. The test chartcomprises a plurality of regions or areas printed at different inkdensities. In particular, the test chart comprises a plurality ofregions printed at successively increasing ink densities. The test chartis printed onto a print media.

An embodiment of a test chart is shown in FIG. 2. The test chart 200comprises the plurality of regions printed at different ink densities.In the embodiment shown in FIG. 2 the regions are columns 210, not allof which are indicated for clarity. Each column 210 is printed at arespective ink density. The ink density of the columns 210 increasessuccessively, from left to right of the test chart shown in FIG. 2. Inthe embodiment shown, the ink density of the columns 210 increases inincrements of 10% beginning from a minimum ink density, which in theexample of FIG. 2 is 60%. Each column 210 is printed having a total andprimary ink limits set according to the respective ink density.

In some embodiments, the test chart 200 is printed using a pre-treatmentlevel applied to the print media prior to printing which is expressed asa percentage of the total ink limit. Therefore the regions in eachcolumn 210 have a different absolute amount of pre-treatment applied tothe media prior to printing, owing to the higher ink limit for columnshaving a higher ink density, whilst the whole chart 200 has the samepre-treatment level applied. Two or more test charts 200 may be printedhaving different pre-treatment levels. The two or more test charts 200may be printed in step 110 by combining several charts 200 havingdifferent pre-treatment levels.

Each column 210 comprises a plurality of sub-regions 220, not all ofwhich are indicated for clarity. In embodiments of the invention for acolour printing device, the sub-regions are each printed to have adifferent colour. A first plurality of the sub-regions 220 may beprinted in each process ink colour of the printing device, such as eachof CMYK. A second plurality of the sub-regions are printed, in someembodiments, in the colours RGB. It will be realised that embodiments ofthe invention may print sub-regions having different colours. A furtherregion may correspond to a combination of all of the inks of theprinting device. Each column may comprise a label indicating therespective ink density of the column for the user's information.

When the test chart 200 is printed a boundary 230 will exist between aregion printed at an ink density below an ink drying threshold of theprinting device and print media and a successive region above the inkdrying threshold. The region above the ink drying threshold will exhibitcharacteristics of insufficient drying, such as improper curing of apolymer ink. Thus the boundary 230 is not part of the test chart 200,but is a boundary between a region of sufficient drying 240 andinsufficient drying 250 of the ink observed by the user. The inkdensities below the boundary 230 are ink densities capable of beingprinted by the printing device without curing or drying defects,although to maximise a gamut for the printing conditions the ink densityimmediately below the boundary 230 is preferably used. Furthermore, inembodiments of the invention wherein two or more test charts are printedat different pre-treatment levels, an optimal pre-treatment level may bedetermined by observing borders between different colour regions withineach test chart 200. The test chart printed at the optimal pre-treatmentlevel will have a minimal amount of artefacts between the regions.Furthermore, the colour regions should appear smooth and uniform at theoptimal pre-treatment level.

In step 120 the printing device receives an indication of the locationof the boundary 230. The indication is provided by the user havingobserved the output test chart 200. The printing device may receive theindication via an interface of the printer itself, such as via one ormore buttons of the printer, or the indication may be received via asoftware program associated with the printer which is being executed bya computing device communicably coupled to the printer.

In some embodiments, in step 130 the printing device receives anindication of the location of the boundary 230 and the test chart 200from amongst the plurality of test charts having the optimalpre-treatment level.

FIG. 3 illustrates a colour pipeline 300 of a contone printing deviceaccording to an embodiment of the invention.

The colour pipeline 300 transforms received print data 301 from an inputcolour space to a printer colour space 302. The colour pipeline 300comprises a colour space convertor 310 and a linearizer 320. The colourspace convertor (CSC) 310 controls colour separation and a total inklimit of the print data. The linearizer 320 controls primary ink limitsof the print data.

The input colour space of the received print data 301 may be RGB or CMYKhaving an associated number of bits-per-pixel (bpp), such as 8 bpp. Theprinter colour space comprises N-channels where N is the number of inksin the printing device. The printing device may be a light dye loadprinting device such as a CMYKcm printing device which comprises lightdye load colourants light cyan (c) and light magenta (m). Light dye loadprinting devices typically comprise more than four colourants.

The number of bits used to represent the input colour space may be lessthan or equal to the number of bits used to represent the printer colourspace. In some embodiments, the printer colour space data has 12 bpp.Furthermore, in some embodiments of the invention the printing devicecomprises a pre-treatment fluid which is applied to the print media andthe application of the pre-treatment may be handled in a similar way tothe colourants and thus the printing device may be a CMYKcmP printingdevice wherein P is the pre-treatment.

The colour pipeline 300 utilises colour resources 311, 321 which aredata used by the colour pipeline 300 to transform the input data 301from the input colour space to the printer colour space of the outputdata 302. The colour resources comprise a colour space look-up table(LUT) 311 and a plurality of linearization LUTs 312, as will beexplained.

The colour space LUT 311 defines the ink usage of each ink. Inembodiments of the invention the LUT 311 converts from 8-bit RGB or CMYKdata to 8-bit N-channel data, where N is the number of inks or fluids ofthe printing device. Thus the respective amount of each ink applied tothe print media for a given input colour is controlled by the colourspace look-up table 311.

In some embodiments of the invention the colour separations are relatedto the amount of pre-treatment applied to the media. Thus colourseparations may be controlled according to the amount of pre-treatmentapplied to the print media. Furthermore, for light and dark ink usage,such as C and c, colour separations may be controlled depending on amaximum amount of ink of these colours. For example, for low inkdensities an amount of light ink usage is controlled to be lower.

The colour space LUT 311 further defines a total ink limit whichcontrols a maximum amount of all inks that is applied to the printmedia.

In some embodiments of the invention the colour space LUT 311 allows thecolour separation and total ink limit to be controlled in step 140according to the ink density selection received in step 120. The LUT 311provides conversion from 8 bit CMYK input data 301 to 8 bit or more Nchannel output data 302, such as CMYKcmP data.

In some embodiments the LUT comprises 9 nodes for each input channelgiving 9⁴ entries. The colour space LUT 311 comprises colour separationsand total ink limits pre-computed for different ink densities andpre-treatment levels which are selected according to the inputs receivedin steps 120 and 130.

Ink limits may be expressed as a volume or weight of ink per unit areaof the print media, for example ml/m⁻² or g/m⁻². The ink limits can alsobe expressed in terms of a number of ink drops per print cell, such as2.5 drops/600 dpi cell, or can also be expressed as a percentage of themaximum amount of ink of a single ink, for example 300% meaning 3 timesthe maximum amount of ink applied for a single colour. In embodiments ofthe invention, the ink densities are expressed also as percentages of anominal condition, for example if 100% refers to a 4 drop total inklimit then 80% ink density refers to 3.2 drops.

The linearization LUTs 321 define the maximum amount of each ink appliedto the print media (primary ink limit) and control the application ofeach ink according to a channel value, for example to control the inkamount to be linear in perception to the viewer. Since the linearizationtables 321 control the application of each ink, one of the plurality oflinearization tables LUTs 312 are selected according to the ink densityreceived in step 120. In some embodiments, one of the linearization LUTs312 may be selected in response to the pre-treatment selected in step130 rather than the colour separations. Thus one of a plurality oflinearization LUTs 312 is selected in step 150 from amongst a pluralityof linearization LUTs pre-computed for different combinations of inkdensity and pre-treatment levels.

FIG. 4 illustrates an operation of a linearization table 321 on acontone print value 302 received from the colour pipeline 300. Referencenumerals 410, 411 indicate a change in primary ink limit applied to theinput colour data 302 illustrating a change in output print valueaccording to the primary ink limit. Reference numerals 420, 421 indicatea change in linearity of a conversion from input to output contonevalues for a specific ink density.

FIG. 5 illustrates a writing system (WS) pipeline 500 of the printingdevice according to an embodiment of the invention. The WS pipeline 500receives the print data 302 output by the colour pipeline 300. The WSpipeline 500 converts the received print data 302 from the printercolour space to 1 or 2 bit N-channel colour space, where N is the numberof inks of the printing device. The WS pipeline 500 also controls theprimary and total ink limits of the printing device. The WS pipeline 500converts image data to dots on the print media and, thus, WS pipelineresources 511, 521 may be controlled according to the received inkdensity and pre-treatment level indications in steps 120, 130.

The WS pipeline 500 comprises a halftone module 510 and a masking module520. The WS pipeline 500 provides print data 521 to a print unit 530 forprinting on the print media.

The halftone module 510 receives the contone print data 302 from thecolour pipeline 300 and uses halftone tables 511 to convert the printdata 302 to halftone levels which are output as halftone print data 511.The halftone levels may be defined by a predetermined number of bits perpixel, such as 2 bpp, to give 4 halftone levels although it will berealised that other numbers of halftone levels may be utilised.

The masking module 520 receives the halftone print data 511 and usesmasking resources 521 to convert the print data 511 to a number of dropsper pixel. In a multi-pass printing mode the masking module 520 alsodetermines a drop sequence defining on which pass each drop is fired.

In embodiments of the invention the ink limits and pre-treatment levelapplied to the print media may be controlled by selecting the halftonedata in the halftone table 511 and masking resources 521 according tothe ink density value received in step 120.

In some embodiments, a drop sequence for the pre-treatment may also becontrolled in response to the pre-treatment value received in step 130.The drop sequence is controlled in embodiments of the invention byselecting one of a plurality of masks for each colourant, and also thepre-treatment in some embodiments of the invention. For example, wherethe colour resources 311, 312 have been computed for a drop sequence of1-2-3, changing the drop sequence to 2-4-6 multiplies the amount ofcolourant or pre-treatment by a factor of 2. Thus the ink limits may becontrolled by selecting one of a plurality of masks to control the dropsequence of the fluid onto the media.

It will be appreciated that embodiments of the invention allow thecolour separations and one or more ink limits of a printing device to becontrolled in response to a received indication of an ink density havingoptimal drying characteristics and, in some embodiments, also an optimalpre-treatment level.

Embodiments of the invention allow a colour separation and ink limits ofa printing device to be controlled without the use of a software RIPexecuted by a computing device associated with the printing device. Thecontrol of the colour separation and ink limit in response to anindication of a region having a suitable ink density printed underrealistic printing conditions, such as on a desired print media, allowsaccurate control of printing parameters for the printing conditions.

It will be appreciated that embodiments of the present invention can berealised in the form of hardware, software or a combination of hardwareand software. Any such software may be stored in the form of volatile ornon-volatile storage such as, for example, a storage device like a ROM,whether erasable or rewritable or not, or in the form of memory such as,for example, RAM, memory chips, device or integrated circuits or on anoptically or magnetically readable medium such as, for example, a CD,DVD, magnetic disk or magnetic tape. It will be appreciated that thestorage devices and storage media are embodiments of machine-readablestorage that are suitable for storing a program or programs that, whenexecuted, implement embodiments of the present invention. Accordingly,embodiments provide a program comprising code for implementing a systemor method as claimed in any preceding claim and a machine readablestorage storing such a program. Still further, embodiments of thepresent invention may be conveyed electronically via any medium such asa communication signal carried over a wired or wireless connection andembodiments suitably encompass the same.

All of the features disclosed in this specification (including anyaccompanying claims, abstract and drawings), and/or all of the steps ofany method or process so disclosed, may be combined in any combination,except combinations where at least some of such features and/or stepsare mutually exclusive.

Each feature disclosed in this specification (including any accompanyingclaims, abstract and drawings), may be replaced by alternative featuresserving the same, equivalent or similar purpose, unless expressly statedotherwise. Thus, unless expressly stated otherwise, each featuredisclosed is one example only of a generic series of equivalent orsimilar features.

The invention is not restricted to the details of any foregoingembodiments. The invention extends to any novel one, or any novelcombination, of the features disclosed in this specification (includingany accompanying claims, abstract and drawings), or to any novel one, orany novel combination, of the steps of any method or process sodisclosed. The claims should not be construed to cover merely theforegoing embodiments, but also any embodiments which fall within thescope of the claims.

The invention claimed is:
 1. A method for use in a printing device,comprising: outputting a test chart comprising a plurality of printedregions at respective ink densities; receiving an indication of aselected ink density; and determining one or more resources of theprinting device according to the selected ink density to control one ormore ink limits and a colour separation of the printing device, whereinthe one or more resources includes a linearization table selected from aplurality of linearization tables, each of the plurality oflinearization tables corresponding to a different combination of inkdensity and pre-treatment level.
 2. The method of claim 1, wherein theresources of the printing device are selected from amongst a pluralityof pre-computed colour resources to select the colour separation and theone or more ink limits, based upon the selected ink density.
 3. Themethod of claim 1, wherein the one or more ink limits comprise a totalink limit of the printing device.
 4. The method of claim 1, wherein thetotal ink limit and the colour separation are selected from a look-uptable according to the received indication.
 5. The method of claim 1,wherein the one or more ink limits comprise a primary ink limit of acolour of the printing device.
 6. The method of claim 5, wherein the oneor more ink limits comprise a plurality of primary ink limits for eachof a plurality of colorants of the printing device.
 7. The method ofclaim 6, wherein the primary ink limit is controlled by selectinglinearization data in response to the indication.
 8. The method of claim7, wherein the resources of the printing device comprise a plurality oflinearization tables and one of the linearization tables is selectedaccording to the received indication.
 9. The method of claim 1, whereinthe resources comprise a plurality of drop sequence masks to control theink limit.
 10. A method, comprising: outputting a plurality of testcharts, each test chart printed at a respective pre-treatment levelapplied to a print media and comprising a plurality of printed regionsat respective ink densities; receiving an indication of a selected testchart from one of the test charts and a selected ink density; andselecting one or more resources according to the selected ink densityand the pre-treatment level corresponding to the selected test chart,wherein the one or more resources includes a linearization tableselected from a plurality of linearization tables, each of the pluralityof linearization tables corresponding to a different combination of inkdensity and pre-treatment level.
 11. A printing device, comprising: atest chart module for controlling the printing device to output one ormore test charts comprising a plurality of printed regions at respectiveink densities and to receive an indication of a selected ink density; acolour space convertor for receiving input contone print data having aninput colour space and outputting print data having a printer colourspace, the colour space convertor being arranged to control a colourseparation of the printer colour space according to the indication ofthe selected ink density; wherein one or more pipeline resources areselected to control one or more ink limits of the printing deviceaccording to the selected ink density, wherein the one or more pipelineresources includes a linearization table selected from a plurality oflinearization tables, each of the plurality of linearization tablescorresponding to a different combination of ink density andpre-treatment level.
 12. The printing device of claim 11, wherein thecolour space convertor comprises a look-up table for converting theinput colour space to the printer colour space, wherein the look uptable is indexed according to the input colour space and the selectedink density to determine the colour separation and one or more inklimits.
 13. The printing device according to claim 11, comprising alinearization module having linearization data for controlling alinearity of the print data, wherein the linearization data is selectedaccording to the indication to control a primary ink limit of the printdata.
 14. The printing device according to claim 11, wherein: thelinearization module is arranged to output a plurality of test charts,each test chart printed at a respective pre-treatment level applied to aprint media and to receive an indication of one of the test charts; andthe colour space convertor is arranged to control the colour separationand the one or more ink limits according to the indicated test chart.